1. Technical Field
The present invention relates to thin film transistors and, more specifically, relates to thin film transistors and other devices including organic semiconductor films.
2. Related Art
Recently, organic semiconductor materials have been widely developed as semiconductor materials for thin film transistors (TFT) (for example, refer to “Yuki Toranjisuta no Hyoka to Oyo (Evaluation and application of organic transistor”, Chapter 1, Zairyo (Material), CMC Publishing Co., Ltd.). The organic semiconductor has advantages that it can be readily formed into a thin film by a simple process, such as coating or vacuum deposition, at a lower processing temperature compared to those in the cases of known TFTs containing amorphous or polycrystalline silicon. A lower processing temperature allows formation of a film on a plastic substrate having low heat resistance, which leads to reductions in weight and cost of a resulting display. Furthermore, various applications of plastic substrates utilizing the flexibility can be expected.
Furthermore, JP-A-2005-302888 discloses an optical sensor having a transparent gate electrode and a transparent gate insulating film.
The present inventors have investigated and developed display devices, such as electronic paper, having organic transistors and have further studied on transistor characteristics for improving the characteristics of resulting devices.
However, in the display devices, disadvantages such as a threshold shift of the transistor or a decrease in mobility of carriers are caused by repeated display. This may be caused by that the carriers are trapped in the organic transistor, specifically, in the interface between an organic semiconductor film and a gate insulating film or in these films, during repeated display, and the trapped carriers cause a change in transistor characteristics.